Novel hydantoin derivatives and salts thereof, the process for the preparation thereof, and medicines containing the same, wherein the hydantoin derivatives are represented by the general formula: ##STR1## wherein X.sub.1 and X.sub.2, which may be the same or different, independently represent a hydrogen atom, a halogen atom, a lower alkyl group or a lower alkoxy group; Y represents an oxygen atom or sulfur atom, R.sub.1 and R.sub.2, which may be the same or different, independently represent a hydrogen atom, a lower alkyl group or phenyl group, or both may form a ring with carbon atoms, excluding the case wherein both R.sub.1 and R.sub.2 are hydrogen atom, and n represents 0 or 1. The novel hydantoin derivatives and salts thereof have excellent effects for the treatment of the complications of diabetes mellitus.